Process of preparing metals or alloys for lithographic printing.



UNITED STATES Patented June 16, 1903.

PATENT OFFICE.

' PROCESS OF PREPARING METALS OR ALLOYS FOR LITHOGRAPHIC PRINTING.

SPECIFICATION forming part of Letters Patent N 0. 731,082, dated J une16, 1903.

Original application filed April 19. 1900, Serial lib-13,466. Dividedand this application filed May 21,1902. Serial No. 108,308. (Nospecimens.)

To to whom it may concern:

Be it known that I, Orro CARL STRECKER, a subject of the Emperor ofGermany, and a resident of Darmstadt, Germany, have invented certain newand useful Improvements in the Process of Preparing Metals or Alloys forLithographic Printing, of which the following is a specification, thisbeing a division of my prior pending application, Serial No. 13,466,filed April 19, 1900.

Metal plates for printing purposes may be coated with a hygroscopiclayer by submitting them as electrodes to an electrolytic process, whichconveys thereto in the form of ions the molecules necessary for theformation of the layer. The desired effect may be obtained byelectrolysis in different ways by an electric current; but it isdifficult to obtain this result by such salts, which as electrolytes aredecomposed by the current and which will produce soluble acid salts onaccount of certain secondary proceedings, and which therefore must beapplied with precaution. The same result can be obtained by applyingthese electrolytes to the metal plates to be treated, in which casesdecomposition of the solutions applied take place in the same way as inthe electrolysis. Such reactions occur when certain complexsnbstancesfor instance, the complex salts in a watery solution-arepoured upon the 'plate to be prepared. A vehement reaction anddevelopment of gases will occur, although this could not be expectedfrom the nature of these salts. The complex salt will be reduced to thecomponents, but in most cases no layer will be formed. In special casesonlya difficult soluble layer is formed having caustic qualities,

and therefore the printing-plates will not be fit for practical use. Byemploying a salt of complex acids, the acids of which would singly forminsoluble compounds with the metals employedfor instance, the complexsalt silico-fiuorid of ammonia-this salt when applied to zinc will bedecomposed in radicals of hydrofluoric acid and silicic acid andammonia, and the silicic acid will neutralize the ammonia. The gasdeveloping during this reaction, as described before, is hydrogen, whichwill cause complicated processes, on account of which soluble acid saltsoccur, and,

as stated above, no useful layer is obtained; but these reactions cannotbe given by simple equations. Therefore the hydrogen has to beeliminated by adding oxidizingsubstances, which will be reduced by thenascent hydrogen, and thereby an absolute solid layer will be producedupon the metal oralloys, as described. The adding of said substanceswill have the result that in the reaction the complex salt is dividedinto simple radicals, of which-one part will be ineffective, While theother part will form with the metal of the plate an insoluble layer.Easily-reduced substances will be preferable to obtain this. In mostcases nitrate of ammonia will be suitable. I will, however, not limit myprocess in this respect, as other oxidizing means or salts may be usedto advantage. The reaction of these proceedings expressed by an equationis as follows, when using silico-fluorid of ammonia and nitrate ofammonia:

The process is carried out as follows: A plate, preferably of zinc,although I may use any metal or alloys, which by their color density andchemical quality allow their practical use, is selected. A zinc plate,best No. 12 of the Belgian gage, is ground by means of a course emeryand pumice powder, equal parts, and a pad made of steel turnings of thefinest and selectest shape. This pad is covered with a soft leather inorderto prevent the fingers from being hurt by cutting them with thesharp edges of thesteel tu rnings. Before grinding, the plate iswashedwith a solution of acid fiuorid of ammonia, three ounces to thegallon of water, and one-fourth of a pint of ammonia in order to removegrease or oxid. Then the zinc is rinsed properly and the plate is groundby passing the pad with a slight pressing and rotative movement over theplate. After having done so for about twenty to twenty-five minutes, thesize of the plate being a yard square, the plate is washed 0E and thenpoured and distributed on it two pints of water acidulatedwith abouteighty drops of nitric acid and then left for about three minutes. Afterthis the plate is washed well-prepared surface,so that the gum touchesand fits the greasy substance. On the dried plate lithophine, a solutionof asphalt in benzene and spirits of turpentine, is poured and thegreasy substance dissolved. The liquid is wiped off so that only verylittle of it is left on the plate and then the latter is dried again.The plate is washed with water to free it from gu'm-arabic, and thenappears with a layer of.

asphaltum on its face. The design is properly inked with printing-ink bythe usual method until a good black negative is obtained. The plate ismade dry and alterations or corrections are made. The plate is againgummed and dried, the gum washed off, and the plate inked up afresh anddried again. Finally, the negative is dusted in with powdered colophane,and this is rubbed ed with talc. Then the plate is ready for theprocess. The zinc plate thus obtained with a copy, or simply ground andwithout a copy, is used for the printing-plate, and the said solution ispoured on the plate. The solution is then distributed by means of a finehair-brush and allowed to act upon the zinc or other metal in the courseof two to three minutes, while the solution is brushed frequently overthe plate to cause it to improve and strengthen the layer. When the timeof action for the chemical substances has passed over, the remainingsolution is washed 0E, the plate is made dry, and is then gummed. Theprocess of coating may berepeated, and finally the plate after gummingis made dry and is then ready for use.

In the case that a plate was furnished with its coating before printingthereon a transfer or design it will be necessary to free it from thegum .which adheres yet and wash the plate well, or wash first with asolution of alum and then with water when zinc was used or with othermeans on other metals, or zinc plates may also be washed with a weaksolution of soda to neutralizethe gum or the reaction of salts used.Then the plate is provided with a design or transfer or the like andtreated with the solution, as before, and is then ready for printingafter having been washed, gummed, and dried subsequently.

The solution applied contains a mixture of salts composed of threeounces of complex salts and three ounces of an oxidizing means and threeounces of gum-arabic in one pint and a half of water, or about four percent. of the salts. The time of the action and the composition of thesolution depends upon the kind of work. When the lithographic negativeor transfer has been well protected by resinous substances, acomparatively strong solution' may be used. As to the complex salts andthe substances which may be applied in these processes, I preferably useof the salts of the complex acids chiefly silicofluorid of ammonia mixedwith nitrate of ammonia in equal parts, by weight.

The result in all cases is the production of an insoluble hygroscopiclayer on the metal employed.

In carrying out my improved process one must be careful to attend to therules given in this specification for producing transfers, as otherwiseit inadvertently occurs that the negative is easily smeared or daubedbefore even my process may be applied.

Having now particularly described and ascertained my invention, what Iclaim, and desire to secure by Letters Patent, is-

The process for preparing'metal plates or alloys for lithographicdesigns, transfers and printing, consisting in submitting the preparedplates to the treatment of a solution containing two to four per cent.of a mixture of salts of complex acids whose constituent acids singlywould form insoluble compounds with the metals employed, and anoxidizing means, which solution, acting on the metal and the latter onthe chemicals applied in the process, forms on the plate an insolubleand hygroscopic layer which is firmly adherent to the surface of themetals or alloys employed, substantially as described.

In testimony whereof I have hereunto set my hand in presence of twowitnesses.

, OTTO CARL STREOKER. Witnesses:

' J EAN GRUND,

CARL GRUND.

